Frequency selective mesh with controllable mesh tuning



on H C R A S p 6 D. F. BOWMAN FREQUENCY SELECTIVE MESH WITH CONTROLLABLEMESH TUNING Filed May 8, 1962 2 Sheets-Sheet 1 J'EE. 1. PIP/0R riffLEA/Gill OF 3708 TUNING ElfAIf/VRS' CONTROLS FRfQl/f/VCY SEZZ C r/ W) YM 1 mw J WM m m r w F 1 a a H U 2. WZL J Y .J M F g F U a W U a F L J .JF F U H U QU 4 J t. a i

. 8, 1964 D. F. BOWMAN FREQUENCY SELECTIVE MESH WITH CONTROLLABLE MESHTUNING I 2 heets-Sheet 2- Filed May 8, 1962 F5 FEEQUEA/C Y fismaelvx,ine-8.6km: Sur s United States Patent 3,148,370 FREQUENCY SELECTIVE MESHWITH CONTROLLABLE MESH TUNING David F. Bowman, Wayne, Pa., assignor toI-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation ofPennsylvania Filed May 8, 1962, Ser. No. 193,671 20 Claims. (Cl.343-756) This invention relates to a frequency selective signalimpinging surface and more particularly to a standard mesh surface inwhich individual portions thereof may be readily modified to vary theirreflection and transmission characteristics to impinging radiation.

In many electronic communication or radar systems it is necessary toprovide a reflecting surface for electromagnetic energy. A typicalexample is the reflector type antenna wherein a suitably shapedreflecting surface acts in conjunction with the illuminating feed toimprove the gain and field pattern of the radiated energy. Aparticularly well known antenna of this type is the parabolic antenna,wherein the signal feed is placed at the principal focus of a parabolicreflecting surface. The parabolic surface thereby concentrates theelectromagnetic radiation of the antenna in the same way that a searchlight reflector produces a sharply defined beam of light. The parabolicreflector accomplishes this by converting the spherical wave originatingat the focus of the parabola into a plane wave of uniform phase acrossthe mouth or aperture of the parabola. Conversely, such an antenna whenused in conjunction with a receiver, concentrates the impinging planewave into a spherical wave at the focus.

It is well known in the art to construct the parabolic reflectingsurface of a sheet metal mesh perforated with apertures in a regulartwo-dimensional pattern. Another mesh surface presently being used isformed of a crossed array of parallel extending wires. The size andspacing of the mesh apertures determine the frequency characteristics ofthe surface. As the hole size or spacing is decreased the signal passband of the surface is raised, thereby raising the upper frequency limitfor good reflection.

In some applications it is desirable to provide a variation of thefrequency characteristics at different portions of the reflectingsurface. Typically this might be desired in a parabolic antenna whereina uniform reflecting surface should preferably be presented to signalsimpinging at either the vertex region or the peripheral region. Sincethe angle of incidence differs at these different portions of thesurface, appropriate modifications would have to be made to the surfaceitself for it to present the same characteristics throughout to a signalemanating at the focus. Attempts have been previously made to sooptimize each portion of the reflecting surface by varying the size andspacing of the apertures at different portions of the surface. Thismethod is, however, quite undesirable because of the increased costinvolved in effecting a special set-up in the manufacture of theoriginal mesh surface. My invention permits such a variation to bereadily obtained from a standard perforated metal sheet or wire meshwithout changing the original spacing between the openings. Thus astandard reflecting surface may be selectively modified to optimize thefrequency characteristics over each portion of its surface after theoriginal manufacture thereof.

Basically the reflecting surface of this invention is constructed of amodified standard mesh surface wherein alternate intersections of themetallic members of the mesh are removed, as by cutting, permitting alength of stub to remain. The presence of these stubs in the newlyformed enlarged mesh openings act as capacitive elements,

3,148,370 Patented Sept. 8, 1964 ice the length of which may be adjustedto change the frequency characteristics of portions of the surface. Thecapacitive loading effect of the controlled length of stub lowers theresonant frequency of its associated portion of mesh surface, therebylowering its transmission pass band. Each enlarged mesh opening can havetwo sets of such capacitive elements which may be independently adjustedto modify the transmission pass band of portions of the surface tohorizontally and vertically polarized waves. Thus, by varying thelengths of the capacitive stubs remaining from the previouslyintersecting surfaces of the standard mesh, the frequencycharacteristics of individual portions of the surface may be selectivelymodified after the original manufacture of such surfaces.

In one exemplary application of my invention, a single parabolicreflecting surface is used in conjunction with a dual feed of signals Fand F located at its principal focus; these signals may be of the sameor different polarities. Should the field patterns of the two signals Fand F differ, the required parabolic reflecting surface to properlyconcentrate their radiation should correspondingly differ. For example,if F has a broader main lobe field pattern than F the parabolicreflecting surface for F should correspondingly extend sufficiently toinclude the main lobe of F However, should this extending portion of thereflecting surface act as a reflector to the F energy it will have thedeleterious effect of permitting the side load energy of F to beincluded in the radiated beam. To avoid this, the extending portion ofthe parabolic surface should preferably permit the transmission of FInasmuch as the angle of incidence of F will progressively increasetowards the furthermost extending peripheral region of the parabolicreflecting surface, the individual portions of this surface must beselectively modified to maintain the centering of the transmission passband about F This may be readily accomplished with my invention bygradually extending the length of the capacitive stubs in this region toprovide increased capacitive loading as the surface progresses towardsthe furthermost peripheral region.

Should the above parabolic antenna system be constructed in accordancewith the previously available reflection surfaces, a speciallymanufactured surface would typically be used wherein the inter-meshspacings are gradually varied to maintain complete transmission withvarying angle of incidence. Alternatively, the transmission pass bandwould be centered about the median angle of incidence, with transmissionbeing incomplete as the angle of incidence varies. Thus this inventionpermits an improved practical construction of a dual signal parabolicantenna system wherein the reflecting surface may be individuallymatched to the field pattern of each of the signals. In a typicalapplication the extending portion of the mesh may be constructed toreflect L band signals (in the vicinity of 1200 megacycles) and transmitX band signals (in the vicinity of 9400 megacycles) In anotherapplication of my invention the sub-dish of a double reflective antenna,such as a Cassegrain or Schwarzschild system, is constructed inaccordance with my invention to provide a reflective surface to one ofthe antenna signals and a transmission surface to another of the antennasignals. In an illustrative Cassegrain embodiment the two signals areintroduced from separate feeds. One feed is at the common focus of bothdishes; the other feed is at the other focus of the hyperbolic subdish.In such a Cassegrain antenna system both signals may be of the samepolarity with the sub-dish surface being selectively adjusted inaccordance with the teachings of my invention to permit completetransmission to only the signal emanating from the common focus.

In a preferred doubly reflective embodiment (illustratively shown in aCassegrain system), illuminating signals may be fed from a dualpolarized feed at the hyperbolic sub-dish focus, with the main parabolicdish producing a twisting of polarization of the incident signal. Thehyperbolical sub-dish of this Cassegrain embodiment would be selectivelyadjusted to provide a different pass band for the two modes ofpolarization employed.

In both Cassegrain embodiments the peripheral region characteristics ofthe hyperbolic sub-dish would preferably be modified with respect to itsvertex region to provide the requisite complete transmission of energyat different angles of incidence.

It is accordingly a primary object of this invention to provide a signalimpinging surface which may be selectively adjusted to modify thefrequency transmission and reflection characteristics of individualportions thereof.

Another object of this invention is to provide a frequency selectivesignal reflecting surface constructed of a standard mesh surfacemodified to contain controllable length capacitive stubs within the meshopenings.

A further object of this invention is to provide a signal reflectionsurface wherein the frequency transmission characteristics of variousportions of a standard mesh surface may be selectively modified afterits original manufacture.

An additional object of this invention is to provide a signal impingingsurface constructed of a standard mesh surface modified to provideadjustable capacitive stubs for selectively varying the frequencycharacteristics of individual portions of the surface.

Still another object of this invention is to provide a signal impingingsurface constructed of a standard mesh surface adjusted to provideadjustable capacitive stubs for independently varying the frequencytransmission characteristics of individual portions of the surface tosignals of different polarities.

Still a further object of this invention is to provide a signalimpinging surface which may be selectively modified to present the sametransmission characteristics to a signal striking different portions ofthe surface at correspondingly different angles of incidence.

Yet a further object of this invention is to provide a parabolicreflecting surface which uniformly transmits a desired signal overportions of the surface having different angles of incidence withrespect to the signal.

A still further object of this invention is to provide a parabolicreflecting surface which uniformly transmits a desired signal overportions of its surface and reflects the same signal over other portionsof its surface.

Another object of this invention is to provide a parabolic reflectingsurface which may be selectively modified to uniformly transmit a signalstriking different portions of the surface at different angles ofincidence, and uniformly reflect another signal similarly striking thesurface.

These as well as other objects of my invention will readily becomeapparent after reading the following descriptions of the accompanyingdrawings in which:

FIGURE 1 is a plan view of a portion of a standard mesh reflectingsurface of the type presently being used.

FIGURE 2 is a plan view of the reflecting surface of FIGURE 1 modifiedin accordance with my invention.

FIGURE 3 is a typical frequency characteristic of the standard meshsurface of FIGURE 1.

FIGURE 4 is a schematic representation of the equivalent electricalcircuit, within the preferable usable band width of principal resonance,of the standard mesh surfaces of FIGURES l and 2.

FIGURE 5 is a typical frequency characteristic of the modified selectedmesh surface of FIGURE 2 adjusted to have a different transmission passband for horizontally and vertically polarized signals.

FIGURE 6 is a simplified illustration of a dual signal parabolic antennaconstructed in accordance with my invention, with the field pattern ofboth signals being shown.

FIGURE 7 is a simplified illustration of a Cassegrain 4 antenna systemutilizing a hyperbolic sub-dish constructed in accordance with myinvention.

FIGURE 8 is a simplified illustration of another Cassegrain antennasystem utilizing a hyperbolic subdish constructed in accordance with myinvention.

Referring initially to FIGURE 1, the standard mesh surface 10 contains aplurality of narrow conductive surfaces 11 respectively separated andshown extending in a horizontal direction. A similar plurality of narrowconductive surfaces 12 extend in a vertical direction. These surfacesrespectively intersect at points 13 to serve as boundaries for squareopenings 14 of dimensions D Mesh surface 10 may be formed of a singlemetallic member constructed of steel, copper, or any other similarmaterial having the requisite conductive and structural qualities for aparticular application. Such a sheet is then perforated to obtainopenings 14 which are preferably, though not necessarily, square.Alternatively mesh 10 may be constructed of a crossed array ofindividual wires 11 and 12 or similar conductive members to form a mesh.The mesh sheet is bent into the desired form, which may typically be aparabolical of revolution.

As it well known in the micro-wave antenna art, mesh surface 10 will actas a low Q circuit to impinging electromagnetic energy. The spacing Hbetween the horizontally extending members 11 determines the propertiesof that portion of the reflecting surface to the transmission ofhorizontally polarized waves. This spacing will not effect thetransmission of vertically polarized waves. Likewise the spacing Vbetween the vertically extending members 12 determines the properties ofthat portion of reflecting surface 10 to the transmission of verticallypolarized waves. Similarly, spacing V will not effect the transmissionof horizontally polarized waves.

Mesh surface 10 has a frequency characteristic to either vertically orhorizontally polarized waves as indicated in FIGURE 3. The mainresonance encompasses a frequency band existing between f and f Thelocation of this band within the frequency spectrum is determined by theintermesh spacing. Also, a number of higher order subsidiary resonancesare obtained beyond frequency f Such higher order resonances have beenfound to have an undesirable effect upon the signal being reflected.Hence, the preferable usable operating range of the mesh within thefrequency spectrum would only extend to f with appreciable reflectiontaking place at frequencies below f Should the horizontal spacing H andthe hole size D correspond to the vertical spacing V and hole size D themesh surface 10 will exhibit the same frequency characteristic for bothhorizontally and vertically polarized waves. Should it be desired thatthe mesh surface have a different characteristic for horizontally andvertically polarized waves, one of these spacings or hole sizes may bemodified accordingly. Also, the spacings V or H may be made to vary atdifferent portions of the mesh to effect a variation of the frequencycharacteristics of the mesh at such different portions. Thus a selectivevariation in the frequency characteristic of individual portions of theprior art surface of FIG- URE 1 may only be effected by changing theintermesh spacings or hole sizes in the original manufacture. This wouldnecessitate a specially manufactured reflecting surface specificallytailored to the requirements of a particular application.

The mesh reflecting surface having the frequency characteristic as shownin FIGURE 3 may be analogized, within the preferable usable band widthof principal resonance, to a low Q equivalent circuit, as schematicallyrepresented in FIGURE 4. This circuit comprises the parallel combinationof inductive element 41 and capacitive element 42. The essence of myinvention, the physical realization of which will be set forth below, isthe addition of a controllable loading capacitor 43 in paralleltherewith. By adjusting capacitor 43 to introduce a controlled amount ofcapacitive loading to the circuit, the

position of the mesh pass band within the frequency spectrum may bevaried. That is, increasing values of capacitor 43 will accordinglylower the transmission pass band of the mesh surface. The capacitorelement 43 will also vary the Q of the circuit. However, such avariation is quite negligible in a reflecting surface in which the passband is approximately centered about the impinging radiation fortransmission, or the frequency of the signal reflected is appreciablylower than f of the pass band.

The physical realization of such an added controllable additionalcapacitor, as schematically shown in FIGURE 4 is shown in FIGURE 2. Themesh surface of my invention is constructed of a standard mesh, as shownin FIGURE 10, modified by removing, as by cutting, the alternateintersections of the members 11 and 12. The newly formed enlarged meshopenings 21 will be of size D D the dimensions of which equal theoriginal opening size D -D plus V or H the original inter-hole spacing.The enlarged spacing H and V between the newly formed openings 21 isequal to twice the spacings V and H of the original openings 14. Withineach of the openings 21 are contained a number of stub elements 22-25formed from the remaining portions of the alternate conductors which hadhad their intersections removed. The presence of such stub-like metallicmembers in the openings of the mesh will have a capacitive loadingeffect, as schematically shown in FIGURE 4, with the length of the stubsdetermining the degree of such loading. Stub lengths 22 and 23 will onlyeffect the transmission characteristic of the mesh with respect to thehorizontally polarized component of the impinging radiation. Likewise,stub lengths 24 and 25 will similarly effect the characteristics of thesurface with respect to the vertical polarized component 4 of theimpinging radiation.

Stub length 22 and 23 within a single aperture 21 would preferably,though not necessarily, be of the same length. Likewise, stubs 24 and 25within a single aperture 21 would preferably be of the same length. Stubpairs 22-23 may be independently adjusted to control the characteristicsof the reflecting surface 20 with respect to a horizontally polarizedwave. Similarly stub pairs 24-25 may be independently adjusted tocontrol the characteristics of surface 20 with respect to a verticallypolarized wave. Also, the stub pairs of each of the apertures 21 may beindependently controlled to selectively vary the frequencycharacteristics of individual portions of surface 20. Thus, it is seenthat my invention permits a presently available standard mesh surface tobe selectively modified at individual portions thereof with respect tosignals of both the same and different polarities.

The mesh surface of FIGURE 20 has been exemplary modified to have agreater amount of additional capacitive loading for horizontallypolarized signals. Thus, the lengths of stubs 22 and 23 is greater thanthe length of stubs 24 and 25. FIGURE 5 depicts the frequencycharacteristic of such a mesh wherein curve B corresponds to the surfacepresented to a horizontally polarized wave and curve C corresponds tothe surface presented to a vertically polarized Wave. The additionalcapacitve loading effect of the horizontal stubs 22-23 is seen to causea lower pass band as shown by curve B.

Reference is now made to FIGURE 6 which illustrates a typicalapplication of my invention in a dual signal parabolic antenna system60. Antenna feed 61 is located at the principal focus of the parabolicreflecting surface 62 which may be a cylindrical parabola or aparaboloid of revolution. Reflecting surface 62 is constructed inaccordance with the teachings of my invention. Feed 61 has two signals Fand F emanating therefrom. For purposes of clarity the field pattern Fis shown in solid lines and that of F is shown in dotted lines. Therequired extent of parabolic surface 62 to reflect all of the main lobeenergy of F is from the vertex 63 to oppositely extending peripheralregions 64 and 64'. Since signal F has a broader main lobe, parabolicreflecting surface 62 would have to extend into peripheral regions 65and 65 to effect reflection of all of the main lobe energy of thatsignal. The presence of a reflecting surface at the furthermostperipheral portions 64 to 65 and 64' to 65' would provide a source ofside lobe reflection for F To avoid this, these furthermost regions aremodified in accordance with my invention to permit complete transmissionof F while reflecting F Since the angle of incidence is progressivelyincreased towards the extremities 65 and 65' of the surface, thecapacitive tuning elements of my invention may be progressively madelonger towards this region to compensate for such variation in the angleof incidence. Signals F and F may be of the same or different polaritieswith the appropriate modifications being made in the tuning elements 22through 25, as discussed above.

FIGURE 7 illustrates one type of a Cassegrain antenna system utilizingmy invention, with it being understood that other doubly reflectivesystems (e.g. Schwarzchild) may similarly be constructed using theteachings of my invention. This antenna system includes a main parabolicdish 71 and a hyperbolic sub-dish 72. Feed 73 of frequency F is locatedat the focus of hyperbolic surface 72, and feed 74 of frequency F islocated at the focus of parabolic surface 71, the latter also being theother focus of sub-dish '72. Surface 72 is constructed in accordancewith my invention to reflect F but completely transmit F The F energyreflected from hyperbolic surface 72 is reflected as if it emanated from74 and Will, therefore, be reflected from parabolic surface 71 in raysparallel to the principle axis 75 of the antenna system. The energy E;emanating from 74, shown dotted for purposes of clarity, is unaffectedby the presence of hyperbolic surface 72 and will, therefore, undergo asimilar reflection from parabolic surface 71 to yield parallel rays. Asdiscussed above the extreme portions of hyperbolic surface 72 willpreferably be modified to provide complete transmission of signal E; asthe angle of incidence varies.

Reference is now made to FIGURE 8 which illustrates a somewhat differentdoubly reflective antenna system also utilizing a hyperbolic sub-dishconstructed in accordance with my invention. This Cassegrain antenna isof the type described in Jasik, Antenna Engineering Handbook,McGraW-Hill, Inc., 1961, pages 25-3 and 25-14. A dual polarized feed 81at a focus of the hyperbolic sub-dish 82 emits signals F and P ofrespectively vertical and horizontal polarization, the latterpolarization being shown dotted for purposes of clarity. Dual feed 81constructed in the manner well known in the art to simul taneously emitboth signals while maintaining a substantial degree of isolation betweentheir separate sources. Parabolic main dish 83 is constructed of apolarization twisting reflection surface as described in theaforementioned reference. Hyperbolic sub-dish 82 is modified to have adifferent frequency characteristic for horizontally and verticallypolarized signals and more specifically in this embodiment has a lowerpass band for horizontally polarized signals, obtained as shown inFIGURES 2 and 5. The vertical polarized signal 84 will be reflected fromthe hyperbolic sub-dish 82 as if it emanated from common focus FReflection by the main parabolic dish 83 converts F to horizontallypolarized waves; thus the waves of F which strike the sub-dish 32 forthe second time will be transmitted therethrough. Similarly thehorizontally polarized signals F are reflected upon initial occurrencewith the hyperbolic sub-dish 82 as if they emanated from the main focus84. Upon reflection by the main dish 82 they will become verticallypolarized, thereby passing through sub-dish 82. Thus, it is seen thatsub-dish 82 provides the double reflection of both signals parallel tothe principal axis 85 and does not im- 7 pede the passage of the doublyreflected signal therethrough.

Thus it is seen that my invention provides a frequency selective signalreflective surface wherein individual portions thereof may beindependently modified to suit the particular requirements of an antennasystem. Specifically, I have illustrated my invention with a parabolicantenna system and two Cassegrain antenna systems. It is naturallyunderstood that the reflective surface of my invention may be utilizedin various other applications wherein selective reflection andtransmission of impinging radiation is desired. Thus, I prefer to bebound not by the specific disclosure herein but only by the appendedclaims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows.

1. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; at least some of saidapertures including a controllable stub tuning element.

2. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; at least some of saidapertures including a controllable stub tuning element formed of aconductive surface substantially similar to said intersecting conductivesurfaces.

3. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; at least some of saidapertures including a controllable stub tuning element formed of aconductive surface substantially similar to said intersecting conductivesurfaces; said stub element being afiixed to one of said intersectingconductive surfaces intermediate the aperture boundaries thereof, andextending towards an oppositely disposed one of said intersectingsurfaces.

4. A signal impinging mesh surface comprising a plurality of aperturesbounded by respectively intersecting pairs of substantially parallelconductive surfaces; at least some of said apertures including a firstpair of controllable stub tuning elements formed of a conductive surfacesubstantially similar to said intersecting conductive surfaces; one ofsaid first pair of stub elements being affixed to a first boundingconductive surface of a first parallel pair of said conductive surfaces,intermediate the aperture boundaries thereof and extending towards asecond bounding conductive surface of said first parallel pair ofconductive surfaces; the other of said first pair of tuning elementsbeing aflixed to said second conductive surface intermediate theaperture boundary thereof, and extending towards said first conductivesurface.

5. The signal impinging mesh surface of claim 4, wherein each of saidfirst pair of stub elements are of equal length and are located midwaybetween the aperture boundaries thereof.

6. A signal impinging mesh surface comprising a plurality of aperturesbounded by respectively intersecting pairs of substantially parallelconductive surfaces; at least some of said apertures including a firstand a second pair of controllable stub tuning elements formed of aconductive surface substantially similar to said intersecting conductivesurfaces; one of said first pair of stub elements being affixed to afirst bounding conductive surface of a first parallel pair of saidconductive surfaces, intermediate the aperture boundaries thereof andextending towards a second bounding conductive surface of said firstparallel pair of conductive surfaces; the other of said first pair oftuning elements being afiixed to said second conductive surfaceintermediate the aperture boundary thereof, and extending towards saidfirst conductive surface; one of said second pair of stub elements beingaffixed to a third boundary conductive surface of a second pair ofparallel conductive surfaces; the other of said second pair of stubelements being afiixed to a fourth boundary conductive of surface Ofsaid second pair of parallel conductive surfaces; said second pair ofparallel conductive surfaces intersecting said first pair of parallelconductive surfaces; said second pair of stub elements beingintermediate the aperture boundaries established by said first pair ofparallel conductor surfaces, and extending towards each other.

7. The signal impinging mesh surface of claim 6, wherein said first pairof stub elements are located midway between said second pair ofconductive surfaces and extend generally parallel thereto; and saidsecond pair of stubelements are located midway between said first pairof conductive surfaces and extend generally parallel thereto.

8. The signal impinging mesh surface of claim 6, wherein each of saidfirst pair of stub elements are of a first equal length; and each ofsaid second pair of stub elements are of a second equal length.

9. A signal impinging mesh surface comprising a plurality of aperturesbounded by respectively intersecting pairs of substantially parallelconductive surfaces; at least some of said apertures including a firstand second pair of controllable stub tuning elements forward of aconductive surface substantially similar to said intersecting conductivesurfaces; one of said first pair of stub elements being afiixed to afirst bounding conductive surface of a first parallel pair of saidconductive surfaces, intermediate the aperture boundaries thereof andextending towards a second bounding conductive surface of said firstparallel pair of conductive surfaces; the other of said first pair oftuning elements being affixed to said second conductive surfaceintermediate the aperture boundary thereof, and extending towards saidfirst conductive surface; one of said second pair of stub elements beingafiixed to a third boundary conductive surface of a second pair ofparallel conductive surfaces; the other of said second pair of stubelements being aifixed to a fourth boundary conductor of surface of saidsecond pair of parallel conductor surfaces; said second pair of parallelconductor surfaces intersecting said second pair of parallel conductorsurfaces; said second pair of stub elements being intermediate theaperture boundaries established by said first pair of parallel conductorsurfaces, and extending towards each other; said first pair of stubelements being located midway between said second pair of conductivesurfaces and extending generally parallel thereto; and said second pairof stub elements being located midway between said first pair ofconductive surfaces and extending generally parallel thereto; each ofsaid first pair of stub elements being of a first equal length; each ofsaid second pair of stub elements being of a second equal length; andsaid first length differing from said second length.

10. A signal impinging surface comprising a first plurality of narrowconductive surfaces, respectively separated and extending in a firstdirection; a second plurality of substantially similar narrow conductivesurfaces respectively separated and extending in a second direction;said first and second surfaces intersecting to form a mesh; eachadjacent pair of intersecting first and second surfaces bounding anaperture; at least some of said apertures including a first controllablestub element afiixed to one of said intersecting first boundary surfacesintermediate the boundary established by said second intersectingsurfaces, and extending towards the other of said intersecting firstsurfaces.

11. A signal impinging surface comprising a first plurality of narrowconductive surfaces, respectively separated and extending in a firstdirection; a second plurality of substantially similar narrow conductivesurfaces respectively separated and extending in a second direction;said first and second surfaces intersecting to form a mesh; eachadjacent pair of intersecting first and second surfaces bounding anopening; at least some of said openings including a first pair ofcontrollable stub elements, each affixed to one of said first surfaces,intermediate the boundary established by said second pair ofintersecting surfaces, and extending towards each other; a second pairof conductive stub elements, each afiixed to one of said sec- 0ndsurfaces, intermediate the boundary established by said first pair ofintersecting surfaces, and extending toward each other.

12. The signal impinging mesh surface of claim 11, wherein each of saidfirst pair of stub elements are located midway between said second pairof intersecting surfaces, and extend generally parallel thereto; each ofsaid second pair of stub elements are located midway between said firstpair of intersecting surfaces, and extend generally parallel thereto.

13. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; said apertures including afirst pair of controllable length stub tuning elements; the length ofthe stub elements in some of said apertures differing from the length inother of said apertures.

14. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; said apertures including afirst and second pair of controllable length stub tuning elements; saidstub element pairs being respectively affixed to oppositely disposedpairs of said intersecting conductive surfaces; said stub element pairsvarying the characteristics of said mesh surface to differentlypolarized signals; the lengths of the stub elements in some of saidapertures differing from the lengths in other of said apertures.

15. An antenna system including a frequency selective reflectivesurface; said reflective surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; at least some of saidapertures including a con trollable stub tuning element.

16. In combination, a parabolic reflecting surface and a dual signalfeed located at a focus thereof; said reflective surface comprising aplurality of apertures bounded by intersecting conductive surfaces; atleast some of said apertures including a controllable length stub tuningelement; and the length of some of said stub elements at the extremeperipheral region differing from the length of said stub elements at thevertex region.

17. In combination, a parabolic reflecting surface and a dual signalfeed located at a focus thereof; said reflecting surface comprising aplurality of apertures bounded by intersecting conductive surfaces; saidapertures including a first and second pair of controllable length stubtuning elements; said stub element pairs being respectively affixed tooppositely disposed pairs of said intersecting conductive surfaces; saidstub element pairs varying the characteristics of said mesh surface todifferently polarized signals emitted by said signal feed.

18. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; said apertures including afirst pair of controllable length stub tuning elements; the length ofthe stub elements in some of said apertures differing from the length inother of said apertures; whereby said mesh surface presents a firstuniform frequency characteristic to a first impinging signal havingdifferent angles of incidence over different portions of said meshsurface.

19. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; said apertures including afirst pair of controllable length stub tuning elements; the length ofthe stub elements in some of said apertures differing from the length inother of said apertures; whereby said mesh surface presents a firstuniform frequency characteristic to a first impinging signal havingdifferent angles of incidence over different portions of said meshsurface and a second uniform frequency characteristic to a second signalsimilarly impinging said mesh surface.

20. A signal impinging mesh surface comprising a plurality of aperturesbounded by intersecting conductive surfaces; said apertures including afirst and second pair of controllable length stub tuning elements; saidstub element pairs being respectively affixed to oppositely disposedpairs of said intersecting conductive surfaces; said stub element pairsvarying the characteristics of said mesh surface to differentlypolarized signals; the lengths of the stub elements in some of saidapertures differing from the lengths in other of said apertures; wherebysaid mesh surface presents a first uniform frequency characteristic to afirst impinging signal having different angles of incidence overdifferent portions of said mesh surface and a second uniform frequencycharacteristic to a second signal similarly impinging said mesh surface,said first and second signals being differently polarized.

No references cited.

1. A SIGNAL IMPINING MESH SURFACE COMPRISING A PLURALITY OF APERTURESBOUNDED BY INTERSECTING CONDUCTIVE SURFACES; AT LEAST SOME OF SAIDAPERTURES INCLUDING A CONTROLLABLE STUB TUNING ELEMENT.